Well, it was basically the only book out at that time. I remember a few others in the 1990s - Compiler Design in C; Holub, and later after I graduated Modern Compiler Implementation in C; Appel).

Hey something cool I found while googling - Holub's book is available as a free download from the author! (https://holub.com/compiler/)

The Dragon Book has flaws but it is also the case where the pioneer catches all the arrows. But the OP asked about unsubstantiated criticisms of the book so I added in the one I remember from my courses - mostly too much on parsing, not enough on everything else. The 2nd compiler course I took didn't even use a textbook, Dragon book or otherwise; it was a handful of papers and a semester-long project on SSA and associated documentation.

I took a professional development course in C from Alan Holub in Berkeley that I think was the base material from that book, ages ago. I can say that a room-full of talented people worked really, really hard to keep up the pace in that course. Like some other classes at UC Berkeley proper, surviving the course says something about you! It was all in portable C, and rigorous.

I took a course in compilers from Hennessy and Ullman at Stanford in the 80's. The course material was a series of papers written by them on various techniques, including a lot of data flow stuff.